1. Field of the Invention
The present invention relates to a method of producing a transversely aligned web in which filaments spun at a high rate are aligned in the transverse direction and an apparatus for implementing the method of the same. The transversely aligned web is utilized as a raw material web of a transversely stretched nonwoven fabric. Further, the transversely aligned web is utilized as a raw material web for producing a cross laminated nonwoven fabric in which a transversely stretched nonwoven fabric is laid on a longitudinally aligned nonwoven fabric or the like so that the aligning directions thereof cross to each other.
2. Description of the Related Art
Most of the conventional nonwoven fabric is a random nonwoven fabric in which alignment of filaments composing the nonwoven fabric is random. Therefore, the tensile strength thereof is weak and the dimension of the product is unstable. As an invention made for improving such drawback which the conventional nonwoven fabric encounters, there can be introduced Japanese Patent Publication No. 36948/91, Japanese Patent No. 2612203, Japanese Patent Publication No. 6126/95 or the like filed by the present applicant. According to the above publications, there is introduced a lamination type nonwoven fabric in which at least two sheets of nonwoven fabric as a raw material are stretched and the sheets of nonwoven fabric are laid on and bonded to one another so that the directions of stretching thereof cross to each other. Also, a method of producing such a nonwoven fabric is introduced in the above publications.
Japanese Patent Publication No. 36948/91 discloses a method of producing nonwoven fabric in which un-oriented filaments are spun to produce a long fiber nonwoven fabric, and the resulting nonwoven fabric is stretched in one direction under a proper temperature so that the fabric tends to contain a larger rate of filament components aligned in one direction. Also in the patent publication, there is disclosed a method in which sheets of nonwoven fabric stretched by the above method are laid on each other so that the stretching directions of the nonwoven fabrics cross to each other.
Further, Japanese Patent Publication No. 36948/91 discloses a method of producing a long fiber nonwoven fabric in which the nonwoven fabric is produced by using un-oriented filaments aligned in one direction. According to the method of producing the long fiber nonwoven fabric, initially, filaments are produced by extrusion through a nozzle which is provided above a screen mesh running in one direction. Then, the filaments are dispersed by a heated airflow which flows spirally. Further, a pair of airflows are created below the nozzle so that the airflows collide with each other. The rotated spun filaments are further dispersed by the spreading airflow resulting from the collision of the airflows. In this case, if the moving direction of the airflows colliding with each other is in parallel with the running direction of the screen mesh, then the spun filaments are dispersed in a direction perpendicular to the running direction of the screen mesh. Thus, dispersed filaments are piled on the screen mesh and a piece of nonwoven fabric can be created on the screen mesh so that a majority of filaments are aligned in the transverse direction of the fabric. In this way, nonwoven fabric mainly containing filaments aligned in the transverse direction is produced. Conversely, if the moving direction of the airflows colliding with each other is substantially perpendicular to the running direction of the screen mesh, then the spun filaments are dispersed in a direction in parallel with the running direction of the screen mesh. Thus, when dispersed filaments are piled on the screen mesh, a piece of nonwoven fabric can be created on the screen mesh so that a majority of filaments are aligned in the longitudinal direction of the fabric. In this way, nonwoven fabric mainly containing filaments aligned in the longitudinal direction is produced.
Japanese Patent No. 2612203 discloses a method of producing a nonwoven fabric in which fibers are blown off together with a fluid from a blowoff nozzle toward an upper surface of a running belt-conveyor, and the fibers are piled so that the fibers can be aligned in one direction on the upper surface of the belt conveyor, thus a web having fiber aligned therein can be produced. According to one example of the method of producing fabric, at least a part of the belt conveyor is bent downwardly in a direction perpendicular to the running direction thereof, and the fluid and fibers are blown off toward the bottom portion of the bent groove portion of the conveyor belt. Then, the fluid blown off from a blowoff nozzle is dispersed in the direction in which the groove of the conveyor belt extends, whereby fibers are aligned in the dispersing direction.
Japanese Patent Publication No. 6126/95 discloses a method of producing a nonwoven fabric in which a spray spinning is employed so that a plurality of filaments are aligned in substantially one direction to form a one-direction aligned nonwoven fabric. According to the method of producing fabric, when a high molecular compound is blown off through a nozzle to spin filaments, the spun filaments are rotated or vibrated in the width direction. Then, at least a pair of airflows substantially bilaterally symmetrical with respect to the side of the filaments are applied to filaments from the side of the filaments at the center of one filament rotated or vibrated, under condition that the rotated or vibrated filament has a draft property of two times or more. Thus, at least a pair of airflows are applied to filaments so that the filaments are dispersed in a direction perpendicular to the spinning direction of the filament while the filament is applied with draft. In this way, filaments are aligned in the direction in which the filaments are dispersed, and the filaments are piled in stratum, and the one-direction aligned nonwoven fabric can be produced.
The nonwoven fabric produced by the above methods has a high tensile strength. Moreover, since the filament composing the nonwoven fabric has a small diameter of 5 μm to 15 μm after subjecting it to the stretching process, its feeling of touch is smooth and the texture is flexible and soft. Furthermore, the nonwoven fabric is glossy and suitable for printing. In other words, owing to the minute filament diameter, the nonwoven fabric is proper texture. In addition, owing to high tensile strength, the nonwoven fabric provides desirable practical utility in spite of the fact that the thickness thereof is small.
Although the nonwoven fabric produced by the above-described methods disclosed in respective publications has a high tensile strength and proper texture, the productivity of the nonwoven fabric according to the above methods is still unsatisfactory. Therefore, it is necessary to improve the productivity for reducing the cost of the nonwoven fabric. For this reason, in order that the productivity of the producing apparatus disclosed in the above publications and the cost is reduced, it is necessary to develop a spinning means for spinning filaments of a transversely aligned web in which filaments are aligned in the transverse direction. Further, in addition to the improvement of productivity in spinning the filaments, it is necessary to enlarge the tensile strength of the transversely aligned web formed of the obtained filaments while the high productivity is maintained.
If the diameter of the filament of the product at the final stage is predetermined, to improve the productivity of the filaments by a single cone restrictively requires to increase the spinning rate of filaments by the single cone. According to a conventional method of spinning filaments at a high rate, as is disclosed in a reference entitled “The Newest Spinning Technology” (edited by Japanese Conference of Fiber Industry) published by High Molecular Publication Union, the limit rate of spinning is 10000 m/min. on an industrial base. When a transversely aligned web having a large width in which filaments are aligned in the transverse direction is produced, it is requested that the filaments are spun at a rate, e.g., 30000 m/min. to 100000 m/min. or more, far exceeding that rate which has been regarded as a limit so far.
However, to produce the nonwoven fabric only at a high productivity is meaningless, i.e., the produced nonwoven fabric shall have a proper characteristic. That is, it is necessary that the diameter of the filaments is small enough to make the fabric have a proper texture as a transversely aligned web. More concretely, it is necessary that the diameter of the filament soon after spinning falls within a range of from 10 μm to 30 μm, more desirably, to 25 μm. Further, if the transversely aligned web formed of filaments is stretched in the transverse direction to produce a transversely stretched web, it is ideal that the transversely stretched web has a tensile strength in the stretching direction of 132.5 mN/tex (1.5 g/d) or more. Desirably, the transversely stretched web is requested to have a tensile strength of 158.9 mN/tex (1.8 g/d) or more. More desirably, the transversely stretched web is requested to have a tensile strength of 176.6 mN/tex (2.0 g/d) or more. Further, since the transversely aligned web or the transversely stretched web is utilized as a nonwoven fabric, the spinning means is requested to produce the web which is free from a defect portion such as pilling due to breaking of filament.